Gypsum, drywall, and other wall boards are typically crushable and brittle, meaning that their integrity can be diminished without proper reinforcement and they are prone to visible damage. Due to the fact they protrude, the corners of wall boards are particularly prone to dents and other damage. Additionally, drywall sheets do not typically come together perfectly at corners. Corners and clean lines are often the first things that people notice about a room and failing or uneven and rough corners leave a negative impression on a building's original design and build. As corners are also where the most damage occurs on drywall, they are important to put together properly with sufficient reinforcement to minimize damage.
In drywall construction, a corner bead is usually used to cover the corners of wall boards. The corner bead provides additional reinforcement and protection for the corner as well as covers an uneven union between the drywall sheets that form the corner. The use of a corner bead can provide for esthetically-pleasing clean corners and can minimize damage to drywall corners, the repair for which can be expensive and labour-intensive.
Corner beads are typically elongated strips of metal or plastic that are folded, curved, or angled along their longitudinal center line to produce a V-shaped or curved cross section, with the portions of the strip on both sides of the center line configured to be adhered to adjacent wall boards where they join at a corner. Sometimes L-shaped corner beads are used where the strip of metal or plastic is folded, curved, or angled at a position offset from the longitudinal center line. Corner beads are made with various angles and corner shapes, including right angles and rounded or “bullnose” corners and can be used for covering both inside (concave) and outside (convex) corners where wall panels meet.
To apply a corner bead to a drywall corner, drywall mud or joint compound is applied via spatula or the like along the relevant surface of the drywall, typically to both sides of the drywall outside corner from end to end and slightly beyond where the edge of the bead will be positioned. A thick layer of joint compound is applied to both sides of the corner and it is then smoothed off with a putty knife. The dry corner bead is then pressed against the coated corner, pressing it into the layer of drywall compound.
Alternatively, the joint compound can be applied directly to the corner bead first, and then the corner bead can be applied to the drywall corner. The conventional method of applying joint compound to corner beads is to do it by hand. To apply a corner bead to a concave corner, drywall mud or joint compound is applied to the outside (convex) faces of the corner bead. To apply a corner bead to a convex corner, joint compound is applied to the concave faces of the corner bead. In either case, the bead is then pressed against the corner, with the joint compound drying and forming an adhesive joint between the corner bead and the drywall corner.
The process of applying joint compound or drywall mud to the corner bead is labour-intensive, time-consuming and very messy, resulting in joint compound on hands, clothing, and other equipment. Additionally, it can be very difficult to apply an even, consistent thickness of joint compound to the corner bead without any dry spots or thin spots to which the corner bead may have difficulty adhering. Uneven or too much joint compound in some spots results in excessive extraneous joint compound oozing from between the wall board corner and the corner bead, and needing to be scraped off with a spatula so that the resulting corner is not uneven. Typically, a sponge, spatula and/or joint knife is used to clear away the excess by, for example, wiping down the corner bead by pressing the spatula against the bead and sliding downward while squeezing out the excess drywall compound. If the amount of joint compound used is very excess, the sponge, spatula, and/or joint knife will need to be cleaned frequently to avoid buildup. After excess joint compound is removed with a spatula or the like, the dry joint compound around the corner bead is then sanded until a smooth corner is achieved.
It can thus take a significant amount of time to apply joint compound to a corner bead and removing excessive amounts of joint compound can result in much mess and wasted time.
Devices meant to aid in applying joint compound to corner beads are typically difficult to clean and expensive. This is because these devices are usually complex with several moving parts. These devices must be cleaned every time they are to be reused, which can be difficult since drywall mud and joint compound dry relatively quickly, making removal difficult, and the various moving pieces and inserts can trap the drying joint compound. These devices must therefore be thoroughly cleaned and rinsed of joint compound before the compound sets and hardens, and before adding a new batch of joint compound.
Expensive devices with moving parts that are difficult to use and clean, making them one-time-use only, are not ideal for the average homeowner or a person interested in do-it-yourself home renovation.